How to embed nested forms in Symfony

Sometimes you may need to embed forms in Symfony with no related entities, no OneToMany or other relation, you can just add a form inside another as you would do with a new field. The reason to do this could be to group the two forms inside a single action to submit all data in one click, for example. These two entities are not mapped to each other, they are just there for the sake of a grouped action.

// Parent form
public function buildForm(FormBuilderInterface $builder, array $options)
{
	// Add nested form
	$builder->add('article', new ArticleNestedType(
		$this->em // Pass parameters to nested form if any
		),
        array('data' => new Article())); // Pass options parameters to nested form
}

In controller, handle data base actions when form is submitted:

if ($form->isValid()) {
    // Persist new Entity
    if (true === isset($form->getData()['article'])) {
        $article = $form->getData()['article'];
        $em = $this->getDoctrine()->getManager();
        $em->persist($article);
        $em->flush();
    }
}

Then in twig to display child form:

{{ form_widget(form.article) }}